Recent federal and local environmental laws require very significant reduction of discharge of harmful gaseous substances into the atmosphere. Chief among such harmful air pollutants are nitrogen oxides (NOx). In response to strict enforcement efforts of these laws, industrial air polluters have made considerable efforts to reduce the amount of these harmful substances into the air in gaseous effluents from industrial or municipal sources. Successful efforts to reduce the concentration of NOx in gaseous effluents often involve reacting the NOx in waste gases with nitrogen-based reducing agents.
Another known method of removing NOX from gas streams involves contacting the NOX with ozone, thereby oxidizing them to higher nitrogen oxides, such as N2O5 and removing the higher oxides from the gas stream by means of aqueous scrubbers.
Specific details of ozone-based NOx oxidation processes are disclosed in U.S. Pat. Nos. 5,206,002; 5,316,737; 5,985,223; and 6,197,268, the disclosures of which are incorporated herein by reference.
Additionally, the Environmental Protection Agency has presented information showing mercury levels in the environment are at levels that are likely to lead to adverse health effects. Coal-fired utility boilers are one of the largest sources of harmful anthropogenic mercury emissions but also include the NOx and SOx emissions sources.
Oxidative air pollution abatement processes have become increasingly important due to stringent air pollution control regulations. Compared to many processes practiced in the industry, the process based on adding ozone to the flue gas is especially attractive to the industry due to its simplicity and ease in integrating with the existing air pollution equipment. The present state of the art with commercially available ozone generators converts only 10 to 12% of oxygen to ozone, thus requiring the supply of oxygen to be 8 to 10 fold to the ozone demand. The power consumption and capital cost rapidly increases when higher conversions are sought from the generators and so do the cooling water requirements. Therefore, ozone is often cost prohibitive in its widespread application as a pollution treatment reagent.